A line of powerful thunderstorms swept across the area yesterday evening with an explosive mix of wind, rain and lightning that tied up traffic, tore down trees and knocked out power to almost 40,000 homes.

Winds gusted as high as 59 miles an hour, hail fell in spots, parts of the area were deluged with more than an inch of rain and at least one man was burned in a lightning strike at a landfill in upper Montgomery County. Lightning also caused a fire at a house in Prince George's County and damaged a building in Arlington. The number of traffic accidents surged.

The storm, triggered by a cold front, rolled eastward along the Route 50 corridor in Fairfax and Arlington counties, toppling trees, snapping power lines, switching off traffic signals and slowing or stopping long lines of cars. A tree that brought down wires at Route 50 and Gallows Road apparently contributed significantly to the rush-hour disruption.

About 22,000 homes were without power in Northern Virginia at one point, with about 14,000 in the Arlington and Alexandria areas and the others in and around Fairfax County, particularly in the Merrifield and Falls Church areas, a Virginia Power spokesman said. Late last night, about 9,000 customers were still without power.

The Potomac Electric Power Co. reported that 17,500 homes lost power at one point, with about 3,100 in Montgomery County, 7,300 in Prince George's County and 7,100 in the District, principally in the Southeast area. By late last night, the Pepco total was 13,000, most in the District.

The house struck by lightning in Prince George's was in the 2200 block of Dawn Lane in Temple Hills, said fire department battalion chief Bobbi Sarra-Hinkson. She said flames in the attic were quickly extinguished by firefighters.

Lightning knocked a tree onto an apartment building roof in the 200 block of North Glebe Road in Arlington, displacing some tenants.

The lightning injury in Montgomery came just before 5 p.m. in the 6100 block of Olney-Laytonsville Road.

Capt. Eric Ramacciotti, of the fire and rescue department, said the man who was injured had been standing near a bulldozer. He was taken to Suburban Hospital, where he was listed in serious but stable condition. He was in pain from hand and foot injuries, but was nevertheless "very lucky," Ramacciotti said.

Maryland State Police in Rockville said hydroplaning resulting from the heavy rains may have caused "a couple" of accidents on state roads in Montgomery County, and a Prince George's County fire official said the weather was to blame for accidents on roads there.

High water in the westbound lanes of Route 66 between the Roosevelt Bridge and Glebe Road forced authorities to divert motorists from the artery, said Ken Baker, a traffic controller with the Virginia Department of Transportation.

He said it appeared that clogged storm drains may have contributed to the problem.

Rainfall in the northern and eastern parts of the area was particularly heavy. At National Airport, according to National Weather Service meteorologist Chris Strong, about 1.3 inches of rain fell in the two hours starting at 5 p.m.

Just at that hour, sheets of rain descended on the office-building canyons of downtown Washington. Pedestrians, apparently forewarned, unfurled umbrellas and dashed for Metro stations, or sheltering doorways and overhangs. Thunder rumbled, and lightning crackled.

On the Mall, the Washington Monument was shut down for an hour and a half as a precaution because of the lightning hazard. Tourists huddled in the visitors center on the grounds. Evening softball games were canceled.

Despite the downpour, the drought that has gripped the Washington area since last year has not ended.

"You're not going to end the drought with one storm," said forecaster Strong.